The present invention relates generally to rotary cutting tools, such as used in drilling, reaming, grinding and burnishing and the like, and more particularly to a novel composite rotary cutting tool and adaptor and method of making same.
It is known in the tool industry to mount a rotatable cutting tool, such as a high speed twist drill, in an adaptor or gripping member so as to form a composite cutting tool. The metal cutting end of the composite tool may comprise a conventional drill bit having a fluted cutting end and a shank end, and having the desired harness and rigidity. The shank end is generally secured, as by welding, brazing or an adhesive, within an axial bore in an adaptor or gripping member having a larger outer diameter than the drill. See, for example U.S. Pat. Nos. 3,751,176, 4,445,810 and 4,679,971.
Composite drill bits of the aforedescribed type offer a number of advantages. A primary advantage particularly related to small diameter drills, such as in the order of 5 mm or smaller, is that the adaptor or gripping member facilitates mounting of the small diameter drill bit in a conventional chuck of a handheld tool or floor-mounted machine tool, whereas a small diameter drill shank without an adaptor might slip into the space between two jaws or otherwise result in a non-concentric mounting. The larger diameter adaptor or gripping member may be made of a softer material than the associated metal cutting end of the tool, thus minimizing wear and damage to the chuck jaws. The gripping member may also contribute to removal of heat from the metal cutting end of the tool caused by friction during a cutting operation.
A significant problem with known composite metal cutting tools lies in the manner of retaining the shank of the metal cutting tool, such as a high speed twist drill, burr, polishing bit or grinding bit, within the corresponding adaptor or gripping member. As disclosed in U.S. Pat. No. 3,751,176 to Von Hollen, welding or brazing the shank of a metal cutting tool to a larger diameter gripping or adaptor member may soften the cutting end so as to substantially reduce the working life of the tool. The composite bit disclosed in the Von hollen patent represents an attempt to overcome the problems inherent in welding or brazing a cutting tool to a larger diameter gripping or adaptor member, by adhesively bonding the cutting tool shank within an axial bore in the gripping member. Von Hollen teaches that the desired bond strength between the cutting tool shank and the gripping member bore may be obtained by making the length of the interengaging surfaces exceed the minimum length required to produce the desired bond strength for a particular set of surface conditions and clearance between the interengaging surfaces. Von Hollen suggests that the maximum strength or load carrying capacity of the adhesive bond may be increased by etching or abrading the interengaging surfaces so as to roughen these surfaces.
A drawback in the various embodiments of composite bits disclosed in the Von Hollen patent is that desired torque resistant adhesive bonding cannot be achieved together with low concentricity run-out and low angularity error on a consistent and economical basis. The present invention addresses these problems by providing a composite cutting tool and adaptor, and method of making the same, wherein the shank of a cutting tool is adhesively secured within an axial bore of an adaptor in a manner to achieve improved torque resistant bonding together with low concentricity run-out and low angularity error.